Lean of peak operation question

[BillL]

Originally Posted by rv6ejguy

VE is the actual mass flow pumped vs. the theoretical mass flow pumped based on the rpm and displacement. The heating of the charge air in the intake tubes either through conduction at the flange or from impingement of the cooling air from the fins above on the steel tube below would be virtually immeasurable given the short time duration the charge air is in the tube between intake strokes, the small surface to volume ratio and low thermal conductivity of the steel.

I don't see that CHT would have any significant effect on how much mass flow is processed through the engine which determined by flow restriction within the head, valves, intake and exhaust systems plus the delta P inlet to outlet (sometimes we'll have favorable or unfavorable acoustic effects helping or hindering VE at certain rpms).

Completely agree.

[rv6ejguy]

I'd also add, to clarify, that once the air passes the throttle plate, it's been inducted and that air will be exhausted a few milliseconds later.

[rdrcrmatt]

Originally Posted by lr172

I do LOP climbs when not in a hurry or when it's cool, producing more power. Don't be afraid, just pull the mixture to known LOP EGTs. The window doesn't move fast and it's not as dangerous as some would have you believe to be outside the window for short periods. Just keep leaning as you climb to maintain your target EGT. I tend to move to LOP climb after 3000' to avoid some risks.

Larry

while at WOT?

[Paddy]

I'll offer that the ram air effect is the primary reason for the (small) increase in MP value at top of climb as the aircraft accelerates after the comparatively slower airspeed during climb. As a result, the mixture gets (a little) leaner once cruise speed is established.

[Carl Froehlich]

Originally Posted by Paddy

I'll offer that the ram air effect is the primary reason for the (small) increase in MP value at top of climb as the aircraft accelerates after the comparatively slower airspeed during climb. As a result, the mixture gets (a little) leaner once cruise speed is established.

Not exactly.

A MP increase by ram air is the same as adding throttle to increase MP. Your servo will add more fuel. Effect on mixture will be in the grass (assuming constant altitude).

Carl

[Paddy]

That's true - fair point, assuming that the servo sensitivity is fine enough to compensate. Consider also the injector bodies are subject to a relatively higher air pressure in the cowling as airspeed increases, so there might be a correlation there with a tiny fraction more air in the atomization stream compared to that in the climb. Interesting to ponder if nothing else...

[DanH]

Originally Posted by Paddy

That's true - fair point, assuming that the servo sensitivity is fine enough to compensate. Consider also the injector bodies are subject to a relatively higher air pressure in the cowling as airspeed increases, so there might be a correlation there with a tiny fraction more air in the atomization stream compared to that in the climb. Interesting to ponder if nothing else...

At WOT the bleed air delta is very low, not that it matters in this context. Pressure increases on both sides of the nozzle (cooling plenum space and within the cylinder head intake tract), thus velocity change doesn't change the delta. There is no additional bleed air to lean the mixture.

[Paddy]

I see that a bit differently, Dan. The bleed air delta is bound to increase as a function of airspeed in a standard induction RV10. This is because the ram air applied to the upper plenum is virtually unimpeded (disregard nacelle inefficiency), compared to the induction path to the engine. The small inlet, air filter, throttle body and relatively complex/curvy path to the cylinder head all contribute to dynamic pressure drop . The faster you go, the larger the delta between plenum and manifold pressure. This is intuitive, however I believe you may have empirical manometer data from your excellent exploration of cowl exit design that would support the numerical relationship between MP and plenum pressure.

[lr172]

Originally Posted by rdrcrmatt

while at WOT?

Yes. I will be WOT and ROP in climb after take off. I stay ROP at the lower altitudes as more power is produced and more risks. Around 3000, I just pull the mixture to a FF of 8 GPH or so. 8 GPH is is 75% power for the 160 HP 320. 8 is a target and I don't worry if I am a bit higher and I don't worry about time spent in the leaning process, though I do it in one session to get where I want to be. I also watch the EGTs to confirm that I have settled into know LOP ranges.

No sudden engine failures nor any indication of detonation or other problems in 600 hours.

Larry

[lr172]

Originally Posted by Carl Froehlich

Not exactly.

A MP increase by ram air is the same as adding throttle to increase MP. Your servo will add more fuel. Effect on mixture will be in the grass (assuming constant altitude).

Carl

From my experience, the servo doesn't compensate in a linear fashion when manually leaned with the mixture control. Next time you are in cruise, add a bit of throttle. You'll notice that you get leaner and leaner the more you add. The mixture adjustment is not linear with air flow based fuel control in the servo. Increases in throttle or MP seem to require enriching the mixture to maintain the same AFR.